Cross-reactivity of monomeric and dimeric biosynthetic human growth hormone in commercial immunoassays.
Commercial kits give different measurements for concentrations of growth hormone (GH, somatotropin) in serum. Most notably, a two-site monoclonal-antibody-based immunoradiometric assay (IRMA) from Hybritech routinely yields lower values than do conventional RIAs in which polyclonal antibodies are used. We used purified dimeric biosynthetic human GH as a model compound to investigate the specificity of five commercial immunoassays for size variants of GH. In all five assays, biosynthetic monomeric GH was significantly more potent than pituitary-derived standard GH supplied with the kits. Dimeric GH was significantly less potent than monomer in four of the five assays, and cross-reactivities varied more than fivefold, from 15% to 84%. Using three commercial kits selected for their specificity for dimeric GH, we measured GH in serum samples from 18 normal adults. The mean GH concentrations in serum--0.7 (Hybritech, IRMA), 1.8 (Diagnostic Products, RIA), and 3.1 (Cambridge, RIA) micrograms/L--differed significantly, but in the same rank order as that obtained in the experiments on dimer cross-reactivity.
Bowsher
R R
RR
Lilly Laboratory for Clinical Research, Eli Lilly & Co., Indianapolis, IN 46285.
Apathy
J M
JM
Ferguson
A L
AL
Riggin
R M
RM
Henry
D P
DP
D000911:Antibodies, Monoclonal; D003429:Cross Reactions; D005188:False Negative Reactions; D013006:Growth Hormone / Q000032:analysis* / Q000276:immunology / Q000592:standards; D006801:Humans; D015592:Immunoradiometric Assay / Q000592:standards; D010446:Peptide Fragments / Q000032:analysis; D011863:Radioimmunoassay / Q000592:standards; D011933:Reagent Kits, Diagnostic / Q000592:standards*; D011994:Recombinant Proteins / Q000032:analysis
D000911:Antibodies, Monoclonal; D010446:Peptide Fragments; D011933:Reagent Kits, Diagnostic; D011994:Recombinant Proteins; D013006:Growth Hormone